Using an urea-SCR (Selective Catalytic Reduction) system is known as a technology for reducing NOx contained in the emissions from an internal combustion engine. This technology provides a selective reduction catalyst in an exhaust passage from an engine for reducing NOx, and provides an urea aqueous solution injection nozzle upstream of the selective reduction catalyst for injecting urea aqueous solution (herein referred to as reductant) in the exhaust passage. The urea aqueous solution injected from the nozzle is thermally decomposed or hydrolyzed into ammonia by heat from exhaust gas, then, the ammonia is adsorbed into the selective reduction catalyst and reduces NOx to give nitrogen (N2) and water (H2O) by a denitrating reaction with NOx in exhaust gas.
Some systems have a particulate filter in an exhaust passage to decrease a particulate matter such as soot contained in the emission. This particulate filter can trap particulate matter in the emission. In this regard, it is known by Japanese Unexamined Patent Application Publication No. 2003-232218 or U.S. Pat. No. 6,805,849 B1, for example that a selective reduction catalyst may be arranged downstream of an oxidation catalyst and a particulate filter to avoid poisoning a selective reduction catalyst with sulfur oxides and/or emitted particulate matter.
However, the inventors herein have discovered the following issue that can occur in a system wherein a selective reduction catalyst reducing NOx in the emission by receiving reductant, such as urea, is arranged downstream of particulate filter along an exhaust passage.
In the case that a particulate filter is provided in an exhaust passage, and when it is determined that an amount of particulate matter trapped in a particulate filter is larger than a predetermined amount, combusting and removing a particulate matter from a particulate trap, which is referred to as filter regeneration, is executed by combusting unburned fuel or using a heater to heat the particulate, for example. However, when particulate matter is combusted and removed from a particulate filter during the regenerating period, a higher temperature exhaust gas flows into a selective reduction catalyst compared to a lower temperature exhaust gas flow into a selective reduction catalyst during a non-regeneration period. As a result, the ability of the catalytic component contained in a selective reduction catalyst may be decreased, resulting in decreased NOx conversion efficiency of a selective reduction catalyst, and unreduced NOx may be emitted into an atmosphere.
This description addresses this issue. In particular, the description can address an issue that may occur when a selective reduction catalyst in the exhaust, receiving reductant, is arranged downstream of a particulate filter along an exhaust passage. The techniques described herein can potentially avoid NOx emitting into the atmosphere even when NOx conversion efficiency of a selective reduction catalyst is decreased during combustion and removal of particulate matter trapped in a particulate filter.
A first aspect of the present description includes a method of controlling a system having an internal combustion engine, a filter arranged in an exhaust passage and capable of trapping particulate matter contained in the exhaust gas from said internal combustion engine, a reduction catalyst arranged in said exhaust passage downstream of said filter and capable of reducing nitrate oxide contained in the exhaust gas with reductant supplied thereto, the method comprising: in a first mode, combusting a first amount of particulate matter trapped in said filter and supplying a first amount of reductant to said reduction catalyst when an amount of particulate matter trapped in said filter is less than a predetermined trapping amount; and in a second mode, combusting a second amount of particulate matter trapped in said filter that is greater than said first amount of particulate matter and supplying a second amount of reductant that is greater than said first amount to said reduction catalyst when an amount of particulate matter trapped in said filter is equal to or greater than said predetermined trapping amount.
This method overcomes at least some of the disadvantages of the above mentioned reference.
When a particulate matter trapped in a particulate filter is combusted and removed from a particulate filter, an amount of reductant supplied to said reduction catalyst can be increased in comparison to an amount of reductant supplied to a reduction catalyst when the particulate matter is not combusted and removed. Accordingly, even though NOx conversion efficiency (e.g., activation level of catalytic component contained in a reduction catalyst), is decreased during particulate matter combustion and removal, supplying an increased amount of reductant can restrain the decrease of the reduction reaction rate, thereby compensating for the decreased activation level of the catalytic component contained in a reduction catalyst, which results in avoidance of NOx release into atmosphere.
In an example embodiment, in said first mode, said first amount of particulate matter is combusted by supplying the exhaust gas of a first temperature to said filter, and in said second mode, said second amount of particulate matter is combusted by supplying the exhaust gas of a second temperature that is higher than said first temperature to said filter.
In one example, an internal combustion engine has a fuel injector which injects fuel directly into a combustion chamber, and wherein an end of fuel injection during a cylinder cycle in said second mode is retarded from that in said first mode.
In one example, this method further comprises, in the first mode, recirculating a first amount of exhaust gas from said exhaust passage upstream of said filter to an intake passage of said internal combustion engine and recirculating a second amount of exhaust gas that is less than said first amount from said exhaust passage upstream of said filter to an intake passage.
This may avoid the introduction of unburned fuel, which should have been burned off by the oxidation catalyst during burn off of the particulate matter in the particulate filter, into an air intake passage via an exhaust gas recirculation conduit. Accordingly, regeneration of the particulate filter can be better achieved by combustion of the unburned fuel.
However, when exhaust gas recirculation (EGR) is stopped, the amount of NOx emission is increased. To prevent this increased NOx emission to an atmosphere, an amount of supplied reductant can be increased when an amount of NOx emission is increased. Accordingly, the NOx reduction reaction with reductant can become sufficient, which results in avoidance of NOx emission into an atmosphere.
That is, during filter regeneration, even if there is a possibility that some NOx emission cannot be purified for two reasons, namely, decrease of NOx conversion efficiency of a reduction catalyst and increase of an amount of NOx emission from internal combustion engine, this example method can avoid NOx emission into an atmosphere.
In another example embodiment, said internal combustion engine has a fuel injector which injects fuel directly into a combustion chamber, and the method further comprises: in said first mode, supplying fuel from said fuel injector to said combustion chamber so that an end of the fuel injection during a cylinder cycle is a first timing during a cylinder cycle and recirculating a first amount of exhaust gas from said exhaust passage upstream of said filter to an intake passage of said internal combustion engine; and in said second mode, supplying fuel from said fuel injector to said combustion chamber so that an end of the fuel injection during a cylinder cycle is a second timing that is later than said first timing during a cylinder cycle and recirculating a second amount of exhaust gas that is less than said first amount of exhaust gas from said exhaust passage upstream of said filter to said intake passage.
In another example embodiment, this method further comprises increasing an amount of reductant supplied to a reduction catalyst as a desired torque of an internal combustion engine increases and increasing an amount of reductant supplied to a reduction catalyst as a speed of said internal combustion engine increases.
Since an amount of reductant supplied to a reduction catalyst is set according to a desired torque or a speed of said internal combustion engine such that an amount of reductant supplied to a reduction catalyst can correspond with an amount of NOx emission from an internal combustion engine that is changed depending on a desired torque or a speed of said internal combustion engine, this can promote a reaction between a reductant and NOx such that an amount of one of them is not much larger than the other, regardless of whether filter regeneration is carried out or not.
In another example embodiment, this method further comprises increasing an amount of reductant supplied to a reduction catalyst as a temperature of exhaust gas in said exhaust passage between a filter and a reduction catalyst increases.
Since an amount of reductant supplied to a reduction catalyst is increased as a temperature of exhaust gas in said exhaust passage between a filter and a reduction catalyst increases, an amount of reductant can be made to correspond with the degree of decrease in NOx conversion efficiency or degree of decrease in activation level of catalytic component contained in a reduction catalyst, which can promote a reaction between a reductant and NOx such that an amount of one of them is not much larger than the other, regardless of whether filter regeneration is carried out or not.
A second aspect of the present description includes a method of controlling a system having an internal combustion engine, a filter arranged in an exhaust passage and capable of trapping particulate matter contained in the exhaust gas from said internal combustion engine, a reduction catalyst arranged in said exhaust passage downstream of said filter and capable of reducing nitrate oxide contained in the exhaust gas with reductant supplied thereto, the method comprising: in a first mode, recirculating a first amount of exhaust gas from said exhaust passage upstream of said filter to an intake passage of said internal combustion engine and supplying a first amount of reductant to said reduction catalyst; and in a second mode, recirculating a second amount of exhaust gas that is less than said first amount of exhaust gas from said exhaust passage upstream of said filter to said intake passage and supplying a second amount of reductant that is greater than said first amount to said reduction catalyst in a second mode.
This method also overcomes at least some of the disadvantages of the above references.
For example, when the first mode is operated when particulate matter trapped in a particulate filter is combusted and removed (e.g., during filter regeneration), this method can avoid introducing unburned fuel to an oxidation catalyst to combust and remove a particulate matter, by rerouting the unburned fuel into an intake air passage via an EGR conduit. Accordingly, this can promote the performance of regeneration of particulate filter with combustion of unburned fuel.
However, when EGR is stopped, an amount of NOx emission is increased. To prevent this increased NOx emission to an atmosphere, an amount of supplied reductant can be increased when an amount of NOx emission is increased. Accordingly, the NOx reduction reaction with reductant can become sufficient, which results in avoidance of NOx emission into an atmosphere.
That is, during filter regeneration, even if there is a possibility that some NOx emission cannot be purified for two reasons, namely, decrease of NOx conversion efficiency of a reduction catalyst and increase of an amount of NOx emission from internal combustion engine, this example method can avoid NOx emission into an atmosphere.
A third aspect of the present description includes a system comprising: an internal combustion engine; a filter arranged in an exhaust passage and capable of trapping particulate matter contained in the exhaust gas from said internal combustion engine; a reduction catalyst arranged in said exhaust passage downstream of said filter and capable of reducing nitrate oxide contained in the exhaust gas with reductant supplied thereto; a reductant supplier which supplies reductant to said exhaust passage upstream said reduction catalyst; and a controller configured to control: in a first mode, said filter to combust a first amount of particulate matter trapped therein and said reductant supplier to supply a first amount of reductant when an amount of particulate matter trapped in said filter is less than a predetermined trapping amount; and in a second mode, said filter to combust a second amount of particulate matter trapped therein that is greater than said first amount of particulate matter and said reductant supplier to supply a second amount of reductant that is greater than said first amount of reductant when an amount of particulate matter trapped in said filter is greater than said predetermined trapping amount.
This system overcomes at least some of the disadvantages of the above mentioned reference in a same manner as first aspect described above.
In one example, said reductant supplier further comprises a tank accommodating urea solution to be supplied to said exhaust passage upstream said reduction catalyst.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.